11

Spherical Spherical Microwave Microwave

ConfinementConfinement

An introduction for TUNL October, 2008An introduction for TUNL October, 2008

Bill RobinsonBill Robinson

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HistoryHistory February 1995: Scientific American article February 1995: Scientific American article

on sonoluminescence and fusion got me on sonoluminescence and fusion got me started looking for exotic energy sourcesstarted looking for exotic energy sources

1996-99; investigated various cold fusion 1996-99; investigated various cold fusion ideas, usually shock waves through hydride ideas, usually shock waves through hydride aerosols; gave up for lots of reasonsaerosols; gave up for lots of reasons

July 2000; started investigating idea of July 2000; started investigating idea of helical antennas in a sphere—and thought helical antennas in a sphere—and thought of coming to NCSU for physicsof coming to NCSU for physics

2003; started interest in Ball Lightning (BL)2003; started interest in Ball Lightning (BL) 2004; began grad school in hopes of 2004; began grad school in hopes of

building a reactorbuilding a reactor

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More HistoryMore History 2004-2006; went through large number of 2004-2006; went through large number of

possible designs with this geometry (including possible designs with this geometry (including Inertial Electrostatic Confinement [IEC]); ended Inertial Electrostatic Confinement [IEC]); ended up with magnetic SMC theory, BL on the side, up with magnetic SMC theory, BL on the side, formal papersformal papers

August 2006; started construction in 102-A August 2006; started construction in 102-A Research II with Dr. Aspnes as advisorResearch II with Dr. Aspnes as advisor

Spring 2007; obvious that magnets are beyond Spring 2007; obvious that magnets are beyond my capacity in cost, manpower, time; found flaws my capacity in cost, manpower, time; found flaws in theory; concentrating on BL and Spherical in theory; concentrating on BL and Spherical Microwave Confinement with no magnetsMicrowave Confinement with no magnets

September 2007; first plasmaSeptember 2007; first plasma October 13 2007; back to SMC as variety of IEC October 13 2007; back to SMC as variety of IEC

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Inertial Electrostatic Inertial Electrostatic ConfinementConfinement

(Ref. 2)

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IEC single potential well IEC single potential well [3][3]

Fig. 2: Single potential well structure. The minimum normalized potential, Ymin, coincides with the core potential, Ycore = Y(r = 0). The fractional well depth, FWD is defined as FWD = 1-Ymin.

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IEC double potential well IEC double potential well [3][3]

Fig. 3: Double spheroidal potential well structure. The double well depth (DWD) is Ypeak – Ymin. Here, Ypeak coincides with Ycore. A double well is much more likely in SMC than the single well.

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Existing IECExisting IEC Large increase of plasma density in potential wells, fosters high Large increase of plasma density in potential wells, fosters high

rate of reaction there; BUT net reaction rate ~ 1/pressurerate of reaction there; BUT net reaction rate ~ 1/pressure IEC with grids cannot (yet) go above Q~10IEC with grids cannot (yet) go above Q~10 -5-5

Big advantages: no Big advantages: no BB fields, easy high T, simple geometry, fields, easy high T, simple geometry, some fusion does occur at center and in mantle (zone between some fusion does occur at center and in mantle (zone between grids)grids)

High T makes advanced fuels tempting but elusive so farHigh T makes advanced fuels tempting but elusive so far IEC operates at too low density for power reactor (need ~10IEC operates at too low density for power reactor (need ~102121

mm-3 -3 in sizable volume) [5]in sizable volume) [5] IEC is the cheapest way to fusion by a very large factor; IEC is the cheapest way to fusion by a very large factor;

reactors are mostly vacuum, thus low mass. reactors are mostly vacuum, thus low mass. Existing grid reactor can be a practical, portable, simple Existing grid reactor can be a practical, portable, simple

neutron source (like the STAR reactor), but not efficient enough neutron source (like the STAR reactor), but not efficient enough yet for sub-critical fission or large-scale transmutation. yet for sub-critical fission or large-scale transmutation. Maximum so far; 2x10Maximum so far; 2x101010 neutrons/sec by Hirsch in the ’60s [6] neutrons/sec by Hirsch in the ’60s [6] and Nebel in late ’90sand Nebel in late ’90s

Other attempts for either gridless IEC or to protect grids Other attempts for either gridless IEC or to protect grids magnetically from collision (Bussard) have failed (new Bussard-magnetically from collision (Bussard) have failed (new Bussard-style experiment might do better but far from break-even)style experiment might do better but far from break-even)

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Critical IEC Scaling Problem: Critical IEC Scaling Problem: 1/n1/n

As density drops, longer mean free path, As density drops, longer mean free path, more acceleration between grids, higher more acceleration between grids, higher energy, increased <energy, increased <vv>, fewer ion-neutral >, fewer ion-neutral collisions, tighter focus at center, more collisions, tighter focus at center, more head-on collisions. [9]head-on collisions. [9]

Thus fusion reactions scale as 1/n instead Thus fusion reactions scale as 1/n instead of nof n22. IEC reactors operate at very high . IEC reactors operate at very high vacuum << fusion reactor range (10vacuum << fusion reactor range (102121mm-3-3))

Might not be true of SMC since mfp of Might not be true of SMC since mfp of runaway electrons are long due to runaway electrons are long due to velocity; acceleration from microwaves velocity; acceleration from microwaves and grids; less focus anywayand grids; less focus anyway

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Critical IEC scaling problem; Power ~ Critical IEC scaling problem; Power ~ 1/1/aa

aa = radius of spherical active zone, = radius of spherical active zone, qq = total = total charge, charge, aa = potential at = potential at r r = = a, na, nee and and nnii are average are average densities in the active zone, densities in the active zone, P P = power from fusion= power from fusion

For grid IECFor grid IEC, q, q = | = |nnee – n – nii| ~ | ~ nnii aa~ q/a ~ n~ q/a ~ nii a a33/a/a22 = n = nii a a22

Since Since aa is within a small range, is within a small range, nnii ~ 1/a ~ 1/a22

P ~ nP ~ nii 22 *Volume, so *Volume, so P ~ 1/aP ~ 1/a Probably NOT true for SMC since source of ions, Probably NOT true for SMC since source of ions,

electrons, and charge balance is not the same as electrons, and charge balance is not the same as for grids; for grids; q q is not ~ is not ~ nnii

Proof of this is the use of ion or electron beams to Proof of this is the use of ion or electron beams to alter the charge/density relationship in grid IEC to alter the charge/density relationship in grid IEC to increase increase PP

Result is IEC devices are very small (a few inches) Result is IEC devices are very small (a few inches) and cannot scale up while SMC probably canand cannot scale up while SMC probably can

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Unavoidable Loss Problems in grid IECUnavoidable Loss Problems in grid IEC Collisions with grids; PCollisions with grids; Pgridloss/P/Pfusion > 3000; particle > 3000; particle

paths MUST cross grids to be confined [5]paths MUST cross grids to be confined [5] Ion upscatter and energetic tail loss time ~10Ion upscatter and energetic tail loss time ~10-3-3 fusion fusion

raterate Ion neutral capture and escape from potential wellIon neutral capture and escape from potential well Fusion reaction products escape, do not heat plasma Fusion reaction products escape, do not heat plasma

(direct energy conversion probably won’t work) [8](direct energy conversion probably won’t work) [8] Ion collisions increase angular momentum and throw Ion collisions increase angular momentum and throw

ions out of dense center region (may not be so bad, ions out of dense center region (may not be so bad, double wells can work)double wells can work)

No way to keep plasma non-thermal; collision x-No way to keep plasma non-thermal; collision x-section >> fusion x-section by factor of at least 10section >> fusion x-section by factor of at least 1055

Bremsstrahlung same or worse as other reactors, makes advanced non-neutronic fuels probablyadvanced non-neutronic fuels probably

impractical (fuel touted as ideal for IEC) Both ion and electron loss times << fusion timeBoth ion and electron loss times << fusion time

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Some recent IEC experimentsSome recent IEC experiments

Richard Nebel’s Los AlamosTriple-gridded POPS IEC1010 n/s, $500 k, 25 kW [4]

Hitachi IEC, Japan, 7 x 107 n/s

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Spherical Microwave Spherical Microwave ConfinementConfinement

An RF-powered variation An RF-powered variation of Electron of Electron Accelerated Inertial Electrostatic Confinement Accelerated Inertial Electrostatic Confinement (EXL IEC) without internal grids for (EXL IEC) without internal grids for conventional fusion reactions (D-D, D-T, conventional fusion reactions (D-D, D-T, proton-proton-1111B?)B?)

Critical point is to reverse outward-flowing Critical point is to reverse outward-flowing electrons by near-field RF and inward-flowing electrons by near-field RF and inward-flowing electron waves before they reach the electron waves before they reach the antennas, instead of requiring transit through antennas, instead of requiring transit through gridsgrids

If this is correct, the existing hardware could If this is correct, the existing hardware could produce large numbers of neutrons. The produce large numbers of neutrons. The concept might be developed for power concept might be developed for power generation in larger and more efficient generation in larger and more efficient reactorsreactors

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SMC Reactor DesignSMC Reactor Design 20 conical, helical antennas for 20 conical, helical antennas for

2.45 GHz RF, 1 wavelength long, 5 2.45 GHz RF, 1 wavelength long, 5 turns; aluminum sphere is turns; aluminum sphere is groundplane groundplane

20 magnetrons (1kW each) fire 20 magnetrons (1kW each) fire from cap bank (-6kV to -4kV), from cap bank (-6kV to -4kV), ~1/10 sec~1/10 sec

Each hemisphere mounted on Each hemisphere mounted on independent framework on castersindependent framework on casters

2 RF shielded windows 2” diameter2 RF shielded windows 2” diameter Polar pipes (1 ¼”) for access, gas Polar pipes (1 ¼”) for access, gas

in/out, probes, sparker, fiberopticin/out, probes, sparker, fiberoptic Might accommodate either Might accommodate either

hemispherical magnets or neutron hemispherical magnets or neutron shields 1 ½ inches off of surface, shields 1 ½ inches off of surface, nearly enclosing the spherenearly enclosing the sphere

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A Tour of the Lab 1A Tour of the Lab 1

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A Tour of the Lab 2A Tour of the Lab 2

Back of rack-mounted control panel and upper capacitor bank

From 5 magnetrons to coax Distributing current to the ‘trons

Video camera

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A Tour of the Lab 3; A Tour of the Lab 3; alternatives alternatives

Spraying ceramicinside hemisphere

Old open coils with freshceramic

Plastic filled coils with sscircular grid, trying shield patterns, effect of ceramic

Testing alternate gridwith teflon disks at base

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Antennas Antennas

Filling old coils with PVC(not a good idea) to preventplasma inside helix Conical helix in plaster

mold for Mark II

Casting coils in epoxy

Removed epoxy cone

Coating cone withsilica compositeceramic

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Mark II Antennas Mark II Antennas

Copper shield

Riveting triangles to baseMounted antennas

Putting onthe shields

Completed Mk II

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Early Video Stills, Ball Lightning (2007)Early Video Stills, Ball Lightning (2007)

1) Sparker explodes aerosol 2) Magnetrons start breakdown

3) One of 3 frames, hot plasma 4) Winding down, helix cores last to cool

Early shot; 3 torr, sparker loaded with flour and graphite; 30 fps; sparkershould be delayed to have maximum during microwave discharge

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Evolving video stillsEvolving video stills

Open coils, thin wire grid Plastic-filled coils; upper shielded, lowershielded and coated with ceramic

Conical helix in epoxy, ceramic, withbare shield; others no shield, SS grid circles

Upper; completed Mark II, middle;bare shield, lower; coil and ceramic

2121

Antennas as eAntennas as e-- accelerators accelerators Antennas are insulated with ceramic and do not short out to Antennas are insulated with ceramic and do not short out to

plasmaplasma Will apply -6 kV (or more) bias to base rings, 4” diameter, 1” Will apply -6 kV (or more) bias to base rings, 4” diameter, 1”

from wall. from wall. Microwaves cause breakdown, rapidly saturates to critical Microwaves cause breakdown, rapidly saturates to critical

density (opaque plasma)density (opaque plasma) Electron cascade bunches in waves and flows toward center; Electron cascade bunches in waves and flows toward center;

same process turns back electrons exiting center same process turns back electrons exiting center Uncoordinated antenna phases now; may be better in phase Uncoordinated antenna phases now; may be better in phase

for inwards-moving spherical wavesfor inwards-moving spherical waves Existing rig; ~5 x10Existing rig; ~5 x1088 e/cycle at ~ e/cycle at ~25 keV25 keV (~0.2 amp) (~0.2 amp)

assuming delivering 5 kW to waves from microwaves assuming delivering 5 kW to waves from microwaves (efficiency of 0.25)(efficiency of 0.25)

Bias on base rings limited to no more than electron wave Bias on base rings limited to no more than electron wave energy ~ virtual cathode potential; 10 kV for D-T reactor, 50 energy ~ virtual cathode potential; 10 kV for D-T reactor, 50 kV for D-DkV for D-D

Ions also bunch in waves, follow eIons also bunch in waves, follow e-- inwards; q inwards; qii(t)= <-q(t)= <-qee(t-(t-)>)> Inner charge during microwave increase; Inner charge during microwave increase;

qqtotaltotal = q = qii - q - qee = - = - dqdqee/dt> (q/dt> (qee = # inner electrons) = # inner electrons) For each 5 microseconds ion delay, can create 1 kV potential if For each 5 microseconds ion delay, can create 1 kV potential if

low electron losslow electron loss

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Current and Future Research Current and Future Research (1)(1)

THEORY;THEORY; see how closely SMC resembles IEC, determine see how closely SMC resembles IEC, determine mechanism of near field and interaction with grid at mechanism of near field and interaction with grid at various pressuresvarious pressures

Determine energy spectrum of slightly non-Maxwellian Determine energy spectrum of slightly non-Maxwellian plasmaplasma

Ion heating; magnetrons are a few MHz out of phase, Ion heating; magnetrons are a few MHz out of phase, causes Landau damping [8]causes Landau damping [8]

Shock dynamics, if they apply, with antennas in phase or Shock dynamics, if they apply, with antennas in phase or random (current setup is random); compression, heatingrandom (current setup is random); compression, heating

Confinement mechanism for electrons in SMC (and Confinement mechanism for electrons in SMC (and maybe Ball Lightning theory?)maybe Ball Lightning theory?)

Investigate EM knots (alternative Maxwell Equation Investigate EM knots (alternative Maxwell Equation solutions)solutions)

Analyze increased depth of potential well via exit of Analyze increased depth of potential well via exit of fusion product ions and ions expelled via POPSfusion product ions and ions expelled via POPS

Effect of antenna synchronization vs. independent Effect of antenna synchronization vs. independent magnetronsmagnetrons

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Current and Future Current and Future Research (2)Research (2)

HARDWARE;HARDWARE; Diagnostic tools are first priority; Diagnostic tools are first priority; computer DAQ, plasma probes, spectrometer, gas computer DAQ, plasma probes, spectrometer, gas analysis, and detectors for x-rays, gammas, alphas, analysis, and detectors for x-rays, gammas, alphas, but concentrating on D-D NEUTRONS for nowbut concentrating on D-D NEUTRONS for now

Upgrade of vacuum system for lower pressures and Upgrade of vacuum system for lower pressures and higher purity of fuel higher purity of fuel

Hard coating on ceramics to avoid dustHard coating on ceramics to avoid dust Improvement of microwave circuit (depends on Improvement of microwave circuit (depends on

funding); single microwave source, phase and funding); single microwave source, phase and frequency control, lower power and losses, CW, better frequency control, lower power and losses, CW, better materialsmaterials

Monolithic ceramic/Invar antennas (expensive!), better Monolithic ceramic/Invar antennas (expensive!), better ceramic on inside of sphere compatible with ceramic on inside of sphere compatible with expansionexpansion

Given time, might try Ball Lightning experimentsGiven time, might try Ball Lightning experiments

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Current and Future Current and Future Research (3)Research (3)

GOALS;GOALS; SMC proven if D-D neutrons are produced SMC proven if D-D neutrons are produced at at all, all, is the critical test, must be done in a shielded is the critical test, must be done in a shielded environmentenvironment

Thesis ASAP (spring 2009) Thesis ASAP (spring 2009) Diagnostics of potential well and plasma Diagnostics of potential well and plasma

temperature, density, kinetics, RF fields, reaction temperature, density, kinetics, RF fields, reaction volume, energy spectrumvolume, energy spectrum

Design of next D-D or D-T reactor as neutron source, Design of next D-D or D-T reactor as neutron source, en route to--? (Might try p-Ben route to--? (Might try p-B11 11 with decaborane)with decaborane)

Determine how SMC scales in size, plasma density, Determine how SMC scales in size, plasma density, and RF power; extrapolate to propose pilot power and RF power; extrapolate to propose pilot power reactorreactor

FUNDING! And a way to continue doing this after FUNDING! And a way to continue doing this after graduation—in this area if possible; post-doc?graduation—in this area if possible; post-doc?

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What I would need at TUNLWhat I would need at TUNL Shielded space (~11’ x 6’ minimum) safe for Shielded space (~11’ x 6’ minimum) safe for

2.45 MeV neutrons, ~ 102.45 MeV neutrons, ~ 1010 10 / sec (with luck!)/ sec (with luck!) 110 AC power, internet, desk/table space near 110 AC power, internet, desk/table space near

the reactor, room for electronics rackthe reactor, room for electronics rack 1.5 liter/min tap water for cooling turbo pump1.5 liter/min tap water for cooling turbo pump Can borrow fast neutron detector from NCSU Can borrow fast neutron detector from NCSU

for short times but better if can use one from for short times but better if can use one from here (and would need guidance on how to use here (and would need guidance on how to use it and MCA…)it and MCA…)

Could be ready to ship the gear in NovemberCould be ready to ship the gear in November

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Appendix A:Appendix A:Periodically Oscillating Plasma Sphere Periodically Oscillating Plasma Sphere

(POPS)(POPS)

(a) Temporal evolution of plasma potential at the center of thevirtual cathode with and without rf modulation. (b) Delay in the virtual cathode destruction due to rf modulation as a function of modulation frequency. (Reproduced from Ref. 4.) This is for just a few hundred volts and 10-6 torr

Uses RF modulation of grids and emitters to oscillate the potential well in resonance with the orbital frequency of the ions to extend life of virtual cathode

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POPS & SMC?POPS & SMC? POPS in grid IEC cannot scale to a reactor since POPS in grid IEC cannot scale to a reactor since

With With rrvcvc = virtual cathode radius, = virtual cathode radius, oo = potential well depth; note = potential well depth; note change in radius and compression ratio change in radius and compression ratio

Resonant frequency:Resonant frequency:

At fusion reactor conditions, 10-30 MHz (D-D); milder plasmas At fusion reactor conditions, 10-30 MHz (D-D); milder plasmas down to kHzdown to kHz

Works by throwing a few ions out of potential well. Might use by Works by throwing a few ions out of potential well. Might use by RF AM modulation of grids or microwaves, or rapidly pulsed RF AM modulation of grids or microwaves, or rapidly pulsed injected beams of electrons or ionsinjected beams of electrons or ions

Grid IEC needs addition of electrons at center to reduce ion space Grid IEC needs addition of electrons at center to reduce ion space charge and allow compression, may also in SMCcharge and allow compression, may also in SMC

2 2 2max min

2

3( / ) ( / )

2i e o

fusion fusionVC

n n r rP v

e r

2

2 oPOPS

VC i

e

r m

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Appendix B:Appendix B:Magnetic SMC, a possible future Magnetic SMC, a possible future

additionaddition Two hemispherical coils, Two hemispherical coils, counter-rotatingcounter-rotating

Uses cylindrical cusp to make Uses cylindrical cusp to make electron cyclotron resonance electron cyclotron resonance (ECR) on spheroidal (ECR) on spheroidal BB isosurface at 875 gaussisosurface at 875 gauss

Could help make plasma Could help make plasma transparent outside plasmoidtransparent outside plasmoid

Would heat electrons at ECR Would heat electrons at ECR surface efficiently and surface efficiently and selectivelyselectively

reactor is constructed to reactor is constructed to accommodate the coilsaccommodate the coils

Expensive and uses a lot of Expensive and uses a lot of power if not superconductingpower if not superconducting

Could funnel reaction Could funnel reaction products out poles and products out poles and equator for direct energy equator for direct energy conversionconversion

Arrows are B field; center circle is plasmoid surface; outer circle is magnet coil

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Magnetic SMCMagnetic SMC

Coil windings in amp-turns for Coil windings in amp-turns for test reactor, one hemisphere test reactor, one hemisphere (other hemisphere is negative (other hemisphere is negative of this)of this)

- 0 . 4 - 0 . 2 0 0 . 2 0 . 4

- 0 . 3

- 0 . 2

- 0 . 1

0

0 . 1

0 . 2

0 . 3

Tickmarks are meters; contours are B field magnitudes; dark circle is 875gauss (ECR); outer circle is magnet; next circle in is pressure wall; dottedcircle is inner end of antennas

1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6 1 7 1 8 1 9 2 0c o i l s

5 0 0 0

1 0 0 0 0

1 5 0 0 0

2 0 0 0 0

2 5 0 0 0

3 0 0 0 0

A m p t u r n s

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ReferencesReferences

1) A. Siebenforcher, Rev. Sci. Instrum. 67(3), March 19961) A. Siebenforcher, Rev. Sci. Instrum. 67(3), March 1996 2) Tom Ligon, Infinite Energy Issue 30, 20002) Tom Ligon, Infinite Energy Issue 30, 2000 3) IEC thesis by Ryan Meyer, U. of Missouri-Columbia December 3) IEC thesis by Ryan Meyer, U. of Missouri-Columbia December

20072007 4) J. Park, R.A. Nebel, S. Stange, Phys. Plasmas 12, 056315 (2005)4) J. Park, R.A. Nebel, S. Stange, Phys. Plasmas 12, 056315 (2005) 5) ”A general critique of inertial-electrostatic confinement fusion 5) ”A general critique of inertial-electrostatic confinement fusion

systems”, Todd Rider, Phys. Plasmas 2 (6), June 1995systems”, Todd Rider, Phys. Plasmas 2 (6), June 1995 6) R. L. Hirsch, J. Appl. Physics 38, 4522 (1967)6) R. L. Hirsch, J. Appl. Physics 38, 4522 (1967) 7) M. Rosenbluth, F. Hinton, Plasma Phys. Control. Fusion 36 (1994) 7) M. Rosenbluth, F. Hinton, Plasma Phys. Control. Fusion 36 (1994)

1255-12681255-1268 8) F. Chen, 8) F. Chen, Plasma Physics and Controlled Fusion,Plasma Physics and Controlled Fusion, 1984 1984 9) “9) “Development of a High Fluence Neutron Source for

Nondestructive Characterization of Nuclear Waste”, M. Pickrell, LANL Technical Report (1999)

M. Bourham, class notesM. Bourham, class notes

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